A power supply device in which a plurality of electronic components are mounted onto a board, suffers from a problem associated with a noise generated from the electronic components in some cases. Thus, various kinds of configurations for reducing influences of noise are discussed. Further, some electronic components generate heat to have a high temperature, and so, also a way of placement of a heat dissipating means for cooling electronic components in a power supply device is discussed (refer to Japanese Unexamined Patent Publication No. 2000-278936, for example).